[Comparison of formulas for intraocular lens power calculation after corneal refractive surgery].

ABSTRACT

Objective: To evaluate the accuracy of five intraocular lens (IOL) power calculation formulas for calculating IOL power in patients with previous myopia-corrected corneal refractive surgery. Methods: In this case series study, a total of 30 eyes of 30 patients who had excimer laser corneal refractive surgery for myopia and subsequent cataract surgery in Qingdao Eye Hospital from April 2020 to October 2022 were included. The Pentacam anterior segment analysis system and IOLMaster were used to measure ocular parameters, including axial length, anterior chamber depth, keratometry, lens thickness, and mean true net power (mTNP). Five formulas were used for IOL power calculation Shammas formula, Olsen formula, SRK/T (mTNP) formula, Haigis-L formula, and Barrett True-K formula. After cataract extraction, we obtained the actual postoperative refraction by measuring the objective refraction. The prediction error was determined as the difference between the actual postoperative refraction and the predicted refraction, and the absolute value of the prediction error was the absolute error. The differences in the calculation errors of the 5 formulas were compared. Results: Regarding the prediction errors, the results of the SRK/T (mTNP) and Olsen formulas were better than those of Shammas and Haigis-L, and the differences were statistically significant (all P<0.05). The proportion of eyes with an absolute error of 0.50 D for Barrett True-K was highest (70%, 21/30), followed by the SRK/T (mTNP) formula (67%, 20/30). The proportions of eyes with an absolute error within 1.00 D for Barrett True-K, SRK/T (mTNP), and Olsen were all over 80%, with 24 eyes, 24 eyes, and 25 eyes, respectively. Conclusions: The Barrett True-K formula showed high accuracy in predicting the refraction after cataract extraction in patients with a history of corneal refractive surgery for myopia. The calculation result of the Haigis-L formula was highly unstable.